Mammalian fatty acid oxidation (FAO) is essential in hepatic in hepatic intermediary metabolism, as a source of ketone bodies, and in energy production in oxidative tissues. Trifunctional protein (TFP), a complex of 4alpha-subunits with long chain 3-hydroxyl-acyl-CoA dehydrogenase (LCHAD) and long chain 2,3-enoyl-CoA hydratase activities and 4 beta subunits, the long chain 3-keto-acyl-CoA thiolase, catalyzes the last three steps of the FAO spiral. These subunits are encoded by linked, but separate, nuclear genes. Tissue-specific and developmental regulation of TFP subunits occurs. Inherited deficiencies of human TFP cause acute metabolic crises of hypoketotic hypoglycemia and fatty liver, a Rye's syndrome-like phenotype, cardiomyopathy, and skeletal myopathy, events often precipitated by stress. A phenotype to isolated LCHAD deficiency is that smothers carrying affected fetuses develop acute fatty liver of pregnancy. We will explore three hypotheses: (i) that coordinate regulation of TFP alpha- and beta-subunit gene expression must occur, (ii) that genotype-phenotype correlations in human complete TFP and isolated LCHAD deficiencies exist and that maternal liver diseases of pregnancy represent toxicity of 3-hydroxyl-fatty acids and fetal-maternal interactions, and (iii) that mutations in either alpha- or beta-subunits cause complete TFP deficiency because complex formation is altered and the mitochondrial quality control apparatus rapidly degrades free subunits. Our aims are to (i) define tissue and cell-type specific expression of TFP subunit protein and mRNAs during normal mouse development and in response to stress, including alterations in diet, fasting, exposure to cold, and exercise, (ii) analyze transcriptional regulation of the TFP gene locus by in vitro transfection and transgenic mouse approaches, (iii) define mutations in pediatric patients with TFP deficiency and in mothers and children with isolated LCHAD deficiency who have acute liver disease, (iv) characterize the pathogenic mechanisms of TFP and LCHAD deficiencies by analyzing effects of mutations in patient cell lines, after expression in bacteria, and by uptake and complex formation by mitochondria in vitro, (v) characterize our mice with TFP alpha-subunit gene ablation and neonatal lethality, and (vi) characterize LCHAD-deficient mice with the common G1528c, alpha-subunit site-specific gene mutation as a maternal liver disease of pregnancy model.